The present invention relates to a fuel electrode for high-temperature solid electrolyte fuel cells and a method of manufacturing the electrode.
Heretofore, nickel/zirconia (Ni/ZrO2) cermets have been employed for fuel electrodes in commercialized high-temperature solid electrolyte fuel cells.
These Ni/ZrO2 cermets are typically produced by the below alternative processes.
(1) A process in which NiO/ZrO2 is sintered and then reduced to provide a Ni/ZrO2 cermet, (e.g. the Ceramatec process described in Proceedings of SOFC-NAGOYA, p.24); and
(2) A process, known as the Westinghouse process, in which ZrO2 in a crude Ni/ZrO2 cermet is caused to grow into spaces between Ni grains by the EVD technique, (Japanese Kokai Patent Publication No. 61-153280).
Aside from the above, porous platinum (Pt) materials obtainable by sintering platinum pastes have been used in ZrO2 sensors and the like or in basic research.
However, the Ni/ZrO2 cermet electrode manufactured by the first-mentioned process is disadvantageous in that when the fuel cell is run over thousands of hours at temperatures near 1,000° C., the Ni grains therein are sintered thus degrading the electrode and ultimately causing exfoliation of the electrode. Increasing the proportion of ZrO2 to avoid this sintering detracts from the performance of the electrode.
The Ni/ZrO2 cermet manufactured by the second process is resistant to sintering and insures a satisfactory electrode performance, but, since it involves an EVD step, the overall manufacturing process is complicated and the cost of manufacture is increased.
The porous platinum electrode is disadvantageous in that the platinum reacts with the impure metal in the fuel and is vaporized in a continuous operation in a reducing atmosphere resulting in early aging of the electrode. Furthermore, platinum is an expensive metal and the manufacture of porous platinum electrodes is costly.